Aleksandar Panov @ DotNet

Math.Round rounds numbers, but in which way?!!

2010-11-19T01:00:00.000-08:00

I was sure I knew how it rounds fractional parts of number and then I got weird results in some import batch.

So, let's look at the example.

  
Math.Round(1.5) //goes to 2, right?
Math.Round(2.5) //goes to 3, right? Wrong!

Go back to method definition on MSDN and read about method definition and return value once more - here.

  
public static decimal Round(
       decimal d
)

"The integer nearest parameter d. If the fractional component of d is halfway between two integers, one of which is even and the other odd, then the even number is returned."

Okay, let's clarify rule.

  
Math.Round(1.5) //goes to 2
Math.Round(2.5) //goes to 2 !!

Very strange rule if you ask me.

Have a nice day.

State management in Windows Phone 7

2010-09-29T04:26:00.000-07:00

There are 2 types of states you want to save on windows phone 7. One is when user leaves your application and another one is when your application is tombstoned (deactivated by launching some other application from shell, like phone is ringing, phone is locked and so on).

In a first case persistent data is saved into Isolated storage. Using of isolated storage is covered deeply in a number of places on net. So, in this case I put as a reference following link.

Small hint: all the data you save to isolated storage must be serializable.

Another hint - how to check is entity seriazable or not -

  
private static bool IsSerializable(T obj)
{
    return ((obj is ISerializable) || (Attribute.IsDefined(typeof (T), typeof (SerializableAttribute))));
}

In a case another app forces your application closing deactivation event occurs and your handler on this event in app.xaml is executed. Keep in mind following - you have only 10 seconds to save your transient data. If you don't save them in 10 seconds data is discarded and exception raises.

Hint: In this case data is saved into IDictionary<string,object> property called State on PhoneApplicationPage class. Keep in mind following - "The state is only accessible during or after the OnNavigatedTo(NavigationEventArgs) method is called. Also during or before the OnNavigatedFrom(NavigationEventArgs) method is called. If you implement it too early or too late it will throw an exception. You should not use this property for excessive storage as there is a limit of 2MB for each page and 4MB for the entire application."

Cheers

Accelerometer readings from WP7

2010-09-09T07:15:00.000-07:00

Recently I've found interesting image which explains how axes values are represented over sensor on windows phone 7 device. Once when you register event handler for ReadingChanged event you'll get values for x,y and z axes over AccelerometerReadingEventArgs argument.

Argument contains property for x, y and z points. The values are expressed in G-forces (1G = 9.81 m/s2), so a value of 1.0 means that the corresponding axis is being pulled with the same force as the gravity in Paris. For example, if Z is -1.0, then the device is lying flat, face up, on a perfectly flat surface. If Z is 1.0, then the device is lying flat, faced down.

Keep in mind that acceleration reading change event occurs very often (50 times per second) and that you deal with a lot of data.

Silverlight Masterclass UK

2010-04-28T01:40:00.000-07:00

by DanM
27. April 2010 19:00

The Silverlight Tour comes to the UK – and it’s called the Masterclass!

This 3 day hands-on training with both designer and developer tracks looks awesome and (uniquely) has two expert trainers per course.

Currently scheduled in London, Manchester, and the Midlands for June, all courses also come with the chance to win an xbox 360, and Silverlight Spy licences!

Early bird discount of £100 if you book in May, and if you are a member of #SLUGUK or #nxtgenug there are additional discounts to be had.

Full Details are here: http://silverlightmasterclass.net

Cheers

Huge entities list in batches?

2010-04-09T01:10:00.000-07:00

Work with huge list of entities in batches? It has been never easier.

Common programming issue –you have list of 10000 integers or entities (bad programming practice!) in generic list and you need to process them in batches of, let’s say, 250 items per batch.

In the past I solved this problem with following algorithm:

- Sort items per some criteria (in most case sort on identifier)

- Take first chunk of data

- Save last processed id into local variable

- While batch size is more than zero

- Process batch

- Take new chunk of data where identifiers are greater than last processed one

- Set new last processed id

Here is listed code snippet:


//sort list
adIds.Sort((number1, number2) => number1.CompareTo(number2));

int lastProcessedId = 0;

List<> tempList = (adIds.Where(item => item > lastProcessedId)).Take(250).ToList();

while (tempList.Count() > 0)
{
markerAds = AdHandler.GetByIDList(tempList); //items processing (in this case grabbing data from db)

lastProcessedId = tempList[tempList.Count - 1];

tempList = (adIds.Where(item => item < lastProcessedId)).Take(250).ToList();
}

It looks like few simple lines of code. By power of linq, anonymous types and group by method in c# 3.0 it can be done even simpler and in less lines of code.


var groups = adIds.Select((id, index) => new {GroupID = index/250, ID = id}).GroupBy(x => x.GroupID);

foreach (var group in groups)
{
markerAds = AdHandler.GetByIDList(group.Select(x=>x.ID).ToList());
}

Variable “groups” contains chunks of 250 items per group. Faster, simpler and better.

Cheers

Few more usefull Windows Phone 7 links

2010-03-26T07:52:00.000-07:00

Programming Guide for Windows Phone

Windows Phone 7 Series UI Design & Interaction Guide

Videos of MIX10 Windows Phone sessions

Getting Started With Windows Phone 7 Series Development

Tip & information:


protected override void OnManipulationStarted(ManipulationStartedEventArgs args)
{
Color clr = Colors.White;
if (args.OriginalSource == txtblk)

....

Original Source tells you in which element finger manipulation has been started.

"Currently, no production devices have been released. As I understand, the devices will start hitting the market Q4 2010 before Christmas" by Chris Bennett.

How to start working with Windows Phone 7

2010-03-20T07:32:00.000-07:00

What do you need to start working with Windows Phone 7:

Downloads:
Windows Phone developer tools - here ~ 320 MB and 1 computer restart

Developer Training Kit - here (includes 4 sample apps). Gives you global picture and ideas what can be done in the future with windows phone 7 platform.

Articles & books:
ScootGu's first blog about windows phone 7 - here

First ever written book about Windows Phone 7 - here

Windows Phone 7 developer blog - headlines are there

Code Samples from msdn - here.

At the end screen from my first windows phone 7 app - Tweeter reader (thanks to scott guthrie)

Cheers

ASP.NET Dropdown Text aligment

2009-09-28T01:42:00.000-07:00

I've tried to find solution for problem on net but I couldn't find it. What I wanted to achieve is to have some items in drop down list moved a bit more to the right.

I tried to accomplished it by adding " " at the moment when I created items but it didn't worked. Those spaces (" ") were not recognized at the moment when items were rendered. Then I tried with double non breaking spaces ( ) but those were rendered like that in front of item's text.

At the end I've got it with:


item.Attributes.Add("style", "padding-left:10px;");

And drop down looks like on image below:

Generally speaking use attributes property whenever you need to apply some styles to items in drop down.

Cheers

jQuery, attr function, colspan and IE7

2009-09-25T01:33:00.001-07:00

For some reason IE& does not apply attributes from attr function to DOM elements in a case when you want to test colspan on some table cell. Colspan is rendered but it looks like IE refuses to apply it. There is a hack which makes wrapper around problem. Don't ask me why, but it works.

Instead of $("#MediaTitleCell").attr("colspan", 4) you should type code from following snippet:


 $("#MediaTitleCell" + queueID).each(function() {
     this.colSpan = 4;
 });

As I say, don't ask me why but it works this way.

Cheers.

How to bind repeater in n columns.

2009-08-13T02:16:00.000-07:00

Great article I found about how to bind repeater in n column table.

Thanks Antonio.

jQuery: Few tips when you work with Tablesorter plugin

2009-07-21T03:03:00.000-07:00

I like Tablesorter plugin. It is very useful. It can save you a lot of time by sorting items on client side instead of any(partial or full) postback to the server. What I discovered is that sometimes it takes time before it starts to work for you. So, here are few tips for you:

* use $.tablesorter.addParser whenever you can. It is useful cause in examples you can find on Tablesorter documentation all examples handle with plain text in cells. In my case I had few spans, images and so on as a content of span.

*In format property of addParser you define what should be done when content of cell is available. Since I like to use jQuery I realize that jQuery is not appliable to content I get. So weird and so strange. After sometime I got it! jQuery requests root html element and content you get from parameter in format function doesn't have root element. So, in order to get content workable with jQuery create something like this
var innerContent = $("<root>" + s + "</root>"). After that you can apply jQuery. As example I provide code snippet:


$.tablesorter.addParser({

        id: 'currencySwiss',

        is: function(s) {

            return false;

        },

        format: function(s) {

            var innerContent = $("<root>" + s + "</root>");

            if (isElectronicProduct === 'False') {

                if ($("span[id$='ctlNetPriceMediaLabel']", innerContent)[0].innerHTML === "") {

                    return 10000000;

                } else {

                    return $("span[id$='ctlNetPriceMediaLabel']", innerContent)[0].innerHTML;

                }

            } else {//electronic product

                if ($("span[id$='ctlNetPriceLabel']", innerContent)[0].innerHTML === "") {

                    return 10000000;

                } else {

                    return $("span[id$='ctlNetPriceLabel']", innerContent)[0].innerHTML;

                }

            }

        },



        type: 'numeric'

    });

Cheers,

Linq : Select minimal element from collection by some criteria.

2009-06-25T01:57:00.000-07:00

This task was a bit tricky for me but at the end I sorted out.

It should look like similar to code snippet below:

List<Price> list = (from prices in ProductPrices where prices.NetPrice == ProductPrices.Min(minPrice => minPrice.NetPrice) select prices).ToList<Price>();

Inner selection sorts all problems :)

Cheers

YSlow ASP.Net problems

2009-06-16T02:56:00.001-07:00

I've recently expired problems with asp.net web page when I realized that for some reason it loads twice per request. Every time I was in debug mode and I reload page either by pressing F5 or by pressing Enter button in firefox I got my breakpoint on Page_Load method hits twice. When I first time open page in browser everything works fine and Page_Load is called only once.

There is couple of steps to follow in this kind of scenario and as usual I started with looking into code. Soon I realized that code can't be a reason for double loading of page since code is pretty simple.

Then I tested web page from other browsers (IE and Chrome) and everything works fine. Ha, it has something to do with Firefox :).

After some time I ran Fiddler in order to trace communication between client and server and again mystery wasn't solved. There was only one call from client to server.

Then colleague told me: "Why don't you check add ons in firefox?"( Roman thanks :) ). As a "crazy about add ons" developer I have more then 15 add ons inlcuded into Firefox. I disabled them all and problem was solved. Ha!. It has something to do with add ons.! :)

I turned off/on every add on I have in firefox and after some time I realize that problem happens only when YSlow is enabled.

And then I realize that YSlow (which I installed a day before and didn't try to use yet) has setting like "Autorun YSlow each time a web page is loaded".

After hour or two problem was solved. Still I don't know why this only happend when I reload existing page.

Cheers, dear readers :)

Download file from some http address from .NET code

2008-10-30T02:16:00.001-07:00

Never easier.

WebClient oClient = new WebClient();
oClient.DownloadFile(source, destination);

Currency format in method ToString()

2008-08-18T02:18:00.000-07:00

As it is documented in msdn documentation when you want to display currency value from some integer, decimal or any other numeric type you can use method ToString() with currency sign ("C") as a method parameter. Based on current culture info assigned to thread ToString method returns well formatted string. But what if you need some sort of customization of formatted value?

For example, the issue I currently working on.

Culture Info: de-CH (swiss german)

int price = 26540

Method price.ToString("C") returns CHF 26'540.00

This is cool and nice but I need a value without decimal places. Searching thorugh documentation and some forums I found it myself. When you won't decimal places use another parameter for ToString() method - "C0" (c zero);

So, solution is price.ToString("C0") . It returns CHF 26'540 without decimal places.

Cheers

Regular Expressions Alternation (Pipe) trick

2008-05-11T23:39:00.000-07:00

I had a problem with RegEx when engine matches more then one option from alternation group.

Example is like this one - I tried to match seasons like summer 2004 or spring 05. Pattern I made worked fine until I jump into problems when more then one option is listed in input string, like spring summer 2005.

First pattern: (?spring|summer|autumn|winter)(\s)?(?(?:\d{4}|\d{2}))
Input Value: spring 2005
Matches: spring 2005

First pattern: (?spring|summer|autumn|winter)(\s)?(?(?:\d{4}|\d{2}))
Input Value: spring summer 2005
Matches: summer2005

In this case I wanted spring 2005 to be matched. With listed pattern that is not possible. Since summer is listed after spring match for spring can not be found by the engine. I had to find a way to skip word summer somehow.

After several different tests I found solution. What I realized is that in input string I have 2 times following pattern (pseudo code) - season + whitespace. From that point it was easy to find make appropriate pattern.

2nd pattern: ((?spring|summer|autumn|winter)(\s))+(?(?:\d{4}|\d{2}))
Input Value: spring summer 2005
Matches: spring summer 2005.

Keep in mind that Season group has in this case two captures (for spring and summer) and in order to spring value you need to call first item in captures collection, like:

m.Groups["Season"].Captures[0].Value.

Also, captures property works fine when there is only one match.

Every time when you get unexpected results from regex engine analyze what are reasons for unexpected result and you will understand better engine that works under regular expressions in .Net.

One great reference for RegEx I use every time when I need to parse some strings:
http://www.regular-expressions.info

Bye until next tip I found :)

Enumerators in drop down.

2008-05-09T05:57:00.000-07:00

There are very useful methods when you need to fill drop down box with values from some enumerator.

For instance, if you have enumerator like this (VB.NET code):

Public Enum FavoriteColours
Red = 1
White = 2
Yellow = 3
Green = 4
Blue = 5
End Enum

you can easily loop through enumerator keys and values and fill drop down control.

Dim enumNames As String() = System.Enum.GetNames(GetType(FavoriteColours))

Dim enumValues As System.Array = System.Enum.GetValues(GetType(FavoriteColours))

For i As Integer = 0 To enumValues.Length - 1
ctrlVehicleTypeDropDown.Items.Add(New ListItem(enumNames(i), & _
Cstr(Cint(System.Enum.ToObject(GetType(FavoriteColours))))))
Next

Generally speaking, you can fill any list type of control directly form enumerator.

Fill free to use it :)

Keep in mind event hadnlers when pass typed dataset over web services.

2008-02-20T01:28:00.000-08:00

Great new feature in .NET 2.0 - Partial class, can make huge problems sometimes.

You are able to add partial class to typed dataset and to set your own methods, event hamdlers, etc. Particulary problem I work on is that for some reason event handlers are not passed over web services. Here is a scenario:

In typed dataset I want to update one field (Field2) in datatable when other field(Field1) is changed. I also want this to happend when user changes something, not in a moment when typed dataset is filled with data.

So, at the end of FillData method, which fills data into typed dataset I write AddHandler (VB.NET) to attach event handler on event raising in a moment when Field1 is changed. This approach works fine on Front End and value in Field2 is updated every time user changed Field1.

Similar scenario should happend on back end when system (in this case COM+ component) changes value in Field1. Field2 value is not changed. Why??

I started with investigation, write some log messages in event log and realase for some reason that event handlers are not triggered becase they don't exists. How is this possbile? In a moment when web service proxy class calls web service method event handlers are in typed data set. A second later they don't exists in back end. ??

After some time I realise what is a problem. Event handlers are not passed to back end system because they are added programmatically in a run time, not in design time. Yes, it is a true. It is hard to belive but it is a true.

When you add event hadnler programmatically (with AddHandler instruction) it is added to your class (entity, business object, whatever) but it is placed into separate place in local memory. This memory location is not contacted when you pass typed dataset to back end.

If you add event handler in design time (with Handles instruction) event handler is placed into some memory location but type dataset has a reference to it during its lifecycle. Strange, but it is true.

Solution could be found with some local variable of boolean type. You set it to false as a first line of your fill typed dataset method and in event handlers you check is this variable true or not. At the end of fill method set variable to tru and everything is fine. Your code works.

The same scenario applies to system dataset since they also have partial class feature.

Example (some sort of pseudo code) - won't work on back end:

Private sub FillData()

'get data from back end

'fill data

Addhandler typedDataSet.Tables("SomeTable").RowChanged, AddressOf SomeEventHandler

End Sub

Private Sub SomeEventHandler(sender as Object, e as RowChangedEventArgs)

End Sub

How it should be implemented:

private loading as Boolean = false

Private sub FillData()

loading = false

'get data from back end

'fill data

loading = true

End Sub

Private Sub SomeEventHandler(sender as object, e as RowChangedEventArgs) Handles typedDataSet.Tables("SomeTable").RowChanged
If loading

'do something

End If

End Sub

Cheers, mates

Once, forever and never again - Ekatarina Velika

2007-11-06T01:33:00.000-08:00

R.I.P to all members of my favorite band, especially to Milan Mladenovic.

If I had a idol in my life that was him.

I never played guitar, I don't know to play any instrument but I know to understand message he sent to us.

I feel rebellious the same way he was. Rebel about system I live in, people I meet....

I meet him only once in bus 16 to New Belgrade. He was standiing in the middle of bus, a meter from me. I was watching him, told him hello. He answerd me with hello too. I will never foget him.

Funeral:

Like it once was:

EKV's hymn:

One of darknest and the best:

Play with angels, you divine.

Milan Mladenovic (1958 - 1994)
R.I.P

Visual Studio 2005 usefull shortcuts

2007-10-25T03:45:00.000-07:00

There is a plenty of useful shortcuts in Visual Studio 2005. I will number only those which I use everyday.

ALT + F + T - Close solution

CTRL + Shift + B - Build project

ALT + W + L - Close all windows

F12 - GoTo Definition !!! very, very useful (instead of selecting item from right mouse context menu)

CTRL + - Go to previous. Return focus to line of code where F12 was called.

CTRL + K + CTRL + K - Add/Remove bookmark to line of code

CTRL + K + CTRL + N - Move to next bookmark

CTRL + K + CTRL + C - Comment line of code

CTRL + K + CTRL + U - Uncoment line of code

CTRL + Space - complete line from intellisense.

MTS 064 Telekom Srbija Sucks!!

2007-10-22T02:32:00.000-07:00

If you are postpaid user of their service you should be able to check at any moment what is your amount for current month, how many free minutes and sms you have for current month, etc.

Of course, in a case of Telekom Srbija nothing is strict and anything can be changed from month to month. Today, October 22th, service 788 still is not in function for current month. So, all postpaid users of Telekom Srbija are not able to check current status of their amount for October. It means no matter how many talks I made and how many sms I send they can not charge my account more then my postpaid model includes by default, since I am not able to check my account, right?

Somewhere else this is true, but not in Serbia.

We have to pay for their mistakes, errors, disfunctionalities.

Try to complain there: :)

http://www.telekom.yu/KONTAKT/Kontakt.aspx

Typed DataSet's identifiers are not updated.

2007-10-18T02:14:00.000-07:00

Recent problem I had is that identifiers in typed datasets are not updated after I send typed dataset over web services to middle tier in order to save them. Business Logic on middle tier saves row from typed dataset and update row's identifier if row is saved successfully. Update identifier is not visible in returned typed dataset although it is send with byref.

I tried to find solution on net witthout success. I couldn't find anything usefull. Interesting is that when typed dataset is send over web as standard one identifiers are updated with new ids.

What helps me from .Net Framework 2.0 is partial class. Partial class gives us ability to add our own methods in Typed DataSets. So, I opened partial class and add conversion to and from standard dataset.

Code looks like:

Partial Class SpecialSelectionDataSet

#Region "Field"

Private _standardDataSet As DataSet

#End Region

#Region "Properties"

Public Property StandardDataSet() As DataSet
Get
If _standardDataSet Is Nothing Then
_standardDataSet = CType(Me, DataSet)
End If
Return _standardDataSet
End Get
Set(ByVal value As DataSet)
_standardDataSet = value
End Set
End Property

#End Region

#Region "Methods"

Public Sub ToTypedDataSet()
Me.Clear()
Me.Merge(_standardDataSet, True, MissingSchemaAction.AddWithKey)
End Sub

#End Region

End Class

After that I called from me form something like this pseudo code:

myWebServiceProxy.Save(SomeTypedDataSet.StandardDataSet)

me.SomeTypedDataSet.ToTypedDataSet

This solution works fine for me since new identifiers are in typedataset after call of web service method and conversion to typed dataset again.

Do you have any suggestion?

Tose Proeski 1981-2007

2007-10-18T01:04:00.000-07:00

Tose Proeski has died in car accident in Croatia. I didn't listen his music. I even don't know any of his songs. What makes me sad is:

He was so young, only 26 years old.
He has a fantastic voice.
He works a lot to improve his singing capabilities.
He works, works and works. Never stops.

Then I tried to find some of his his songs on youtube. I never heard that someone sings "Zajdi, Zajdi" so beautifully. That song is old Macedonian song which is very hard for singing and even harder for translation. Ask some ex yu citizen to translate you with meaning. No way. His voice can be compared with voices of some of greatest opera singers. Really sad.

Tose sang "Zajdi, Zajdi"

Goodbye superstar.